Vacuum insulated glass (vig) window unit with reduced seal height variation and method for making same

ABSTRACT

A vacuum insulated glass (VIG) window assembly and method for making same is provided in which a variation in the final edge seal height is preferably 0.20 mm or less, more preferably about 0.15 mm or less. Controlling final edge seal height variations substantially reduces breakage of the glass substrates of the VIG window assembly during vacuum pump-down of the cavity between the glass substrates. Edge seal height variation may be controlled, for example, by controlling initial dispensing of green frit material, controlling temperature variations during firing, and/or controlling cycle times during firing.

TECHNICAL FIELD

This disclosure relates generally to vacuum insulated glass (VIG) windowunit configurations and methods for making a VIG window unit. Thedisclosure more particularly relates to configurations of the VIG windowunit edge seal and methods for applying an edge seal material to reducevariations in final edge seal height to reduce the likelihood ofbreakage of the VIG window unit in the vicinity of the edge seal duringa pump-down procedure used to evacuate a cavity formed between glasssubstrates and defined by a perimeter of the edge seal of a VIG windowunit. The disclosure also relates to a structural arrangement anddimensional sizing of the unit for reducing an amount of variation(e.g., a tolerance) in edge seal height prior to evacuation of thecavity.

BACKGROUND AND SUMMARY OF EXAMPLE EMBODIMENTS

Vacuum insulating glass (VIG) units typically include at least twospaced apart glass substrates that enclose an evacuated or low-pressurespace/cavity therebetween. The substrates are interconnected by aperipheral edge seal and typically include spacers between the glasssubstrates to maintain spacing between the glass substrates and to avoidcollapse of the glass substrates that may be caused due to the lowpressure environment that exists between the substrates. Some exampleVIG configurations are disclosed, for example, in U.S. Pat. Nos.5,657,607, 5,664,395, 5,657,607, 5,902,652, 6,506,472 and 6,383,580, thedisclosures of which are all hereby incorporated by reference herein intheir entireties.

FIGS. 1 and 2 illustrate a typical VIG window unit 1 and elements thatform the VIG window unit 1. For example, VIG unit 1 may include twospaced apart substantially parallel glass substrates 2, 3, which enclosean evacuated low-pressure space/cavity 6 therebetween. Glass sheets orsubstrates 2,3 are interconnected by a peripheral edge seal 4 which maybe made of fused solder glass, for example. An array of supportpillars/spacers 5 may be included between the glass substrates 2, 3 tomaintain the spacing of substrates 2, 3 of the VIG unit 1 in view of thelow-pressure space/gap 6 present between the substrates 2, 3.

A pump-out tube 8 may be hermetically sealed by, for example, solderglass 9 to an aperture/hole 10 that passes from an interior surface ofone of the glass substrates 2 to the bottom of an optional recess 11 inthe exterior surface of the glass substrate 2, or optionally to theexterior surface of the glass substrate 2. A vacuum is attached topump-out tube 8 to evacuate the interior cavity 6 to a low pressure, forexample, using a sequential pump down operation. After evacuation of thecavity 6, a portion (e.g., the tip) of the tube 8 is melted to seal thevacuum in low pressure cavity/space 6. The optional recess 11 may retainthe sealed pump-out tube 8. Optionally, a chemical getter 12 may beincluded within a recess 13 that is disposed in an interior face of oneof the glass substrates, e.g., glass substrate 2. The chemical getter 12may be used to absorb or bind with certain residual impurities that mayremain after the cavity 6 is evacuated and sealed.

VIG units with fused solder glass peripheral edge seals 4 are typicallymanufactured by depositing glass frit, in a solution (e.g., frit paste),around the periphery of substrate 2 (or on substrate 3). This glass fritpaste ultimately forms the glass solder edge seal 4. The other substrate(e.g., 3) is brought down on substrate 2 so as to sandwichspacers/pillars 5 and the glass frit solution between the two substrates2, 3. The entire assembly including the glass substrates 2, 3, thespacers/pillars 5 and the seal material (e.g., glass frit in solution orpaste), is then heated to a temperature of at least about 500° C., atwhich point the glass frit melts, wets the surfaces of the glasssubstrates 2, 3, and ultimately forms a hermetic peripheral/edge seal 4.

After formation of the edge seal 4 between the substrates, a vacuum isdrawn via the pump-out tube 8 to form low pressure space/cavity 6between the substrates 2, 3. The pressure in space 6 may be produced byway of an evacuation process to a level below atmospheric pressure,e.g., below about 10⁻² Torr. To maintain the low pressure in thespace/cavity 6, substrates 2, 3 are hermetically sealed. Small highstrength spacers/pillars 5 are provided between the substrates tomaintain separation of the approximately parallel substrates againstatmospheric pressure. As noted above, once the space 6 betweensubstrates 2, 3 is evacuated, the pump-out tube 8 may be sealed, forexample, by melting its tip using a laser or the like.

After evacuation of the cavity to a pressure less than atmospheric,sealing of the pump-out tube may be accomplished by heating an end ofthe pump-out tube that is used to evacuate or purge the cavity to meltthe opening and thus seal the cavity of the VIG window unit. For exampleand without limitation, this heating and melting may be accomplished bylaser irradiation of the tip of the pump-out tube.

In some instances breakage of the VIG unit glass in the vicinity of theedge seal during the cavity evacuation process was observed. Significanttime and resources were expended in an effort to determine the cause ofsuch breakage during cavity evacuation. It was ultimately recognizedthat seal height variations may be related to the breakage problems. Forexample, it may sometimes be the case that the material used to form theedge seal, such as, for example, an adhesive containing frit material,or the like, may include too large of variations in height about theperimeter of the seal that defines the cavity. After conducting numerousexperiments, it was surprisingly found that a correlation existedbetween the seal thickness variation tolerance and instances of breakageduring the cavity evacuation (or pump-down) process. It was alsosurprisingly found that these variations in seal height influence theamount of stress on the VIG units in the vicinity of the seal during theprocess of evacuating the cavity formed between the glass substrates ofthe VIG unit. This evacuation process may sometimes be referred to as apull-down or pump-down procedure. It was also surprisingly found thattoo large of variations in the seal height sometimes results insufficient stress during pump-down that the glass of the VIG unit insidethe perimeter of and generally in the vicinity of the seal would break.For example, and without limitation, too much variation of the sealheight resulted in a gap between the pillars or spacers and at least oneof the glass substrates, which allowed the glass substrate to bend orflex during pump-down. The glass was found to break if the variation inseal height about the perimeter of the seal was too great.

It was also found that there may be several causes for resulting largeseal height variations. These may include, for example, and withoutlimitation, the degree of uniformity of the initial application of green(e.g., unfired) seal material (e.g., frit), and warping or bending ofthe glass substrates during the firing process. Both of these conditionswere found to contribute to a large degree of variation (e.g.,non-uniformity) of final seal height.

To overcome drawbacks associated with glass breakage due to glassbending or flexing during pump-down, it was further determined thatreducing variations in seal height about the perimeter of the edge sealresulted in mitigating the stress (e.g., reducing an amount of bend orflex in the glass substrate) on the VIG unit during pump down andreduced the instances of breakage of the VIG unit glass duringpump-down. As a result of experimentation, seal height variation ortolerance was able to be reduced to small levels by, for example, andwithout limitation, controlling the initial dispensed height of the sealmaterial (e.g., frit material), controlling the flow of the sealmaterial during firing and controlling temperature uniformity during thesealing process. For example, and without limitation, it was found thatcontrolling final edge seal height variations to preferably be less thanabout 0.20 mm, more preferably less than about 0.15 mm and even morepreferably less than about 0.10 mm, resulted in significantly reducedglass breakage during pump-down. It may also be advantageous to providea firing process that reduced warping of the glass substrates duringfiring and controlled and also controlled flow of the seal material,which may also contribute to reducing edge seal height variation.

In order to achieve lower final edge seal height variations, theinventors found, for example, and without limitation, that controllingthe initial dispensed height of the unfired seal material using amachine application process provided significantly improved final sealheight uniformity such that the final seal height variations are inacceptable ranges as noted above. In addition, for example, controllingtemperature uniformity during firing reduced the amount of warping orbending of the glass substrates, further reducing variations in finalseal height. Moreover, controlling the flow of the seal material duringfiring, for example, also improved the final seal height variations,such as, for example, by performing a longer firing process that allowsthe seal material to flow to match the height of the pillars/spacersduring firing.

These and other advantages are provided by a vacuum insulated glasswindow unit comprising: a first substrate and a second substrate; a sealmaterial sandwiched between the first and second substrates and defininga periphery of a cavity formed between the first and second substrates,and forming a hermetic seal between the first and second substrates,wherein a variation in a height of the seal material around the lowpressure cavity is preferably less than about 0.20 mm, more preferablyless than or equal to about 0.15 mm, and even more preferably less thanor equal to about 0.10 mm.

Further advantages are provided by a method of making a vacuum insulatedglass window unit comprising: depositing a seal material on a firstsubstrate, said seal material having a perimeter, the seal materialbeing deposited by a machine and having an unfired height in a range ofabout 0.6 mm to 0.9 mm; and firing a subassembly comprising said firstsubstrate, a second substrate and the seal material sandwiched betweenthe first and second substrates to provide a vacuum insulated glasswindow unit subassembly having a fired seal material height variation ofpreferably less than about 0.20 mm, more preferably less than or equalto about 0.15 mm, and even more preferably less than or equal to about0.10 mm.

These and other embodiments and advantages are described herein withrespect to certain example embodiments and with reference to thefollowing drawings in which like reference numerals refer to likeelements, and wherein:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional schematic diagram of a conventional VIGunit;

FIG. 2 is a top plan view of a conventional VIG unit;

FIG. 3 is a schematic partial cross sectional diagram illustrating anedge portion of an example VIG unit according to an example embodiment;and

FIG. 4 is a flow chart illustrating a method of making a VIG unitaccording to certain example embodiments wherein various processconditions including, for example, seal material height are controlled.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

Certain example embodiments will be described in detail herein withreference to the foregoing drawings in which like reference numeralsrefer to like elements. It will be understood that the embodimentsdescribed herein are intended to be illustrative, not limiting, and thatthose skilled in the art will understand that various modifications maybe made without departing from the true spirit and full scope of theclaims appended hereto.

With reference to FIG. 3, a schematic cross sectional view of a portionof an example VIG window unit 1 is illustrated. The VIG window unit 1includes spaced apart first and second transparent glass substrates 2, 3that may be interconnected by an edge seal 4, which may, for example,and without limitation, be of or include a vanadium based or VBZ typeseal or a solder glass type seal. Example vanadium based or VBZ typeseal compositions are disclosed in U.S. patent application Ser. No.13/354,963, filed Jan. 20, 2012, the disclosure of which is incorporatedby reference herein in its entirety. VBZ (e.g., vanadium, barium, zinc)based seal compositions are discussed in Ser. No. 13/354,963, and may beused for the edge seal 4 in certain example embodiments. Conventionalsolder glass frit material may also be used for the edge seal 4 incertain example embodiments. When using VBZ type seal compositions, alower temperature sealing thermal profile is used to maintain thedesired temper of the glass of the VIG unit because VBZ compositionshave a lower firing temperature (e.g., <250° C.) than certain otherconventional glass frit compositions (e.g., about 500° C.) that may beused to form seals in VIG units. It will be understood that theembodiments disclosed herein are equally applicable to VIGconfigurations using any suitable seal material. As noted above, theperimeter of the edge seal 4 defines a hermetically sealed cavity 6between the substrates that is evacuated as described above.

In certain embodiments, the transparent glass substrates 2, 3 may beapproximately the same size. However, in certain other exampleembodiments, one glass substrate may be larger than the other toprovide, for example, an approximately L-shaped step proximate an edgeof the VIG unit. One or both of the glass substrates 2, 3 may alsooptionally include at least one coating material (not shown), such as,for example, and without limitation, a low-E coating. It will beunderstood that various coatings may be present on an interior surfaceof at least one of the glass substrates 2, 3, and that such coatingsprovide various beneficial performance characteristics to the VIG windowunit 1. In certain example embodiments, the VIG window unit has avisible transmission of at least about 30%, more preferably of at leastabout 40%, even more preferably of at least about 50%, and even morepreferably of at least about 60% or 70%.

An array of support pillars/spacers 5 may also be included between theglass substrates 2, 3 to maintain the spacing of the substrates in viewof the lower than atmospheric pressure that is ultimately provided incavity 6 between the substrates 2, 3. In certain example embodiments,the spacers may have a height, for example, of about 0.1 to 1.0 mm, morepreferably from about 0.2 to 0.4 mm. The height of the spacers maydefine the height of the vacuum cavity 6. As noted above, the spacers 5are preferably of a size that is sufficiently small so as to be visiblyunobtrusive. According to certain example embodiments, the spacers maybe made of or include solder glass, glass, ceramic, metal, polymer, orany other suitable material. Additionally, the spacers 5 may be, forexample, generally cylindrical, round, spherical, dime-shaped, C-shaped,pillow-shaped or any other suitable shape.

A pump-out tube (not shown in FIG. 3) is used in a process to evacuatethe cavity 6 between the substrates 2, 3, such as, for example, byattaching a vacuum pump to the pump-out tube and evacuating the cavityto a low pressure, e.g., a pressure lower than atmospheric pressure. Ina preferred example, a pressure in the cavity 6 is, for example,preferably below about 10⁻² Torr, and more preferably below about 10⁻³Torr, and even more preferably below about 5×10⁻⁴ Torr. After evacuatingthe cavity 6, the pump-out tube may be sealed, for example, by meltingthe tip of the tube by any suitable means, such as, for example, bylaser. VIG window units may be used, for example, and withoutlimitation, as windows in residential homes, office buildings, apartmentbuildings, doors, and/or the like.

According to certain example embodiments, variations in seal height arecontrolled to mitigate the stress (e.g., reducing an amount of bend inthe glass substrate) on the VIG unit during pump down and thus reduceinstances of breakage of the VIG unit glass during pump-down. As aresult of extensive experimentation, seal height variation or tolerancewas able to be reduced by, for example, and without limitation, bycontrolling the initial dispensed height of the seal material (e.g.,frit material), controlling the flow of the seal material during firingand/or controlling temperature uniformity during the sealing process.For example, and without limitation, it was found that controlling finaledge seal height variations to preferably be less than about 0.20 mm,more preferably less than about 0.15 mm and even more preferably lessthan about 0.10 mm, resulted in significantly reduced breakage duringpump-down. “Variation” can be considered to be a difference between amaximum seal height and a minimum seal height. Thus, around the entireperiphery of the edge seal surrounding the low pressure cavity, themaximum height of the edge seal varies from the minimum height of theedge seal by less than 0.20 mm, more preferably less than about 0.15 mmand even more preferably less than about 0.10 mm. According to certainexample embodiments, for example, and without limitation, seal heightvariations may be reduced by providing a machine application processthat more closely controls the initial dispensed height of the sealmaterial (e.g., frit). In addition, to reduce warping or bending of theglass substrates of the VIG window unit that may contribute to finaledge seal height variations, a more controlled firing process, such as,for example, having less temperature variations and/or a longer firingtime may be used. In addition, according to further example embodiments,a longer firing process may be used to control the flow of the sealmaterial during firing, such as, for example, by allowing the sealmaterial to flow to more closely match the height of the pillars orspacers during firing, providing further reduction in seal heightvariation.

According to certain example embodiments, a method of making a VIGwindow unit is disclosed. According to certain example methods, initialseal height material application may be controlled using a machine fordispensing of the initial seal material on one of the glass substratesof the VIG unit. The initial dispensed seal material height may dependupon the type of process used for subsequent firing. For example, andwithout limitation, initial seal material deposition for short-waveinfrared (SWIR) firing may preferably have a green unfired (e.g.,measured dry) frit (e.g., seal material) height in a range of about 0.4mm to 0.9 mm, or more preferably in a range of about 0.5 mm to 0.8 mm,and even more preferably about 0.6 mm to 0.7 mm. Because of therelatively short time used for SWIR processing, the tolerance of initialgreen frit height deposition is lower than in the case of a longer cyclefiring process. For example, and without limitation, for longer cycleconvention type firing, for example, green unfired frit heights maypreferably be in a range of about 0.4 mm to 1.0 mm, or more preferablyabout 0.5 mm to 0.9 mm, and even more preferably about 0.6 mm to 0.9 mm,due to longer peak heating times that allows the seal material to flowor settle down to the height of the pillars or spacers. According tostill further embodiments, the thermal cycle may be controlled toprovide additional control or reduction in seal height variation by, forexample, reducing the amount of warping or twisting of the glasssubstrates of the VIG unit. For example, differentials in temperaturemay cause the glass substrates to warp and twist, resulting in furtherdisadvantageous seal height variation. Therefore, according to certainexample embodiments, firing conditions may be controlled to provide, forexample, greater temperature uniformity (e.g., <2.0° C.) and sufficientheating time (e.g., 20-30 minutes) to allow the glass to stabilize andflatten by allowing the glass substrates to reach even temperature andflatten.

Referring back to FIG. 3, the final seal height H of the edge seal 4 isshown. According to certain example embodiments, variations in theheight H of the edge seal 4 along the perimeter of the edge seal 4 ofthe VIG unit 1 may be controlled, for example, and without limitation,by controlling variations in the initial dispensed height of the sealmaterial (e.g., frit). As noted above, preferred example initialdispensed frit height may depend, for example, on the type of processused to fire the VIG unit. According to certain example embodimentsusing a SWIR type firing process, the initial dispensed seal materialheight may preferably be, for example, in a range of about 0.4 mm to 0.9mm, or more preferably in a range of about 0.5 mm to 0.8 mm, and evenmore preferably about 0.6 mm to 0.7 mm. According to other exampleembodiments using, for example, a longer cycle convention type firing,the initial dispensed seal material height (e.g., green unfired fritheight) may preferably be in a range of about 0.4 mm to 1.0 mm, or morepreferably about 0.5 mm to 0.9 mm, and even more preferably about 0.6 mmto 0.9 mm. The variations in the longer cycle convention type processesmay be larger because this type of firing process may typically havelonger peak heating times. According to example embodiments, the initialfrit dispensing may be performed using a machine process due to theclose tolerances set forth with respect to the above exampleembodiments. Moreover, according to certain example embodiments, it maybe preferable to have longer peak heating times to facilitate flow ofthe seal material during firing and facilitate flattening of the glasssubstrates to further assist in reducing variations in final sealheight. In addition, as noted above, differentials in temperature maycause the glass substrates to warp and twist, resulting in furtherdisadvantageous seal height variation. Therefore, according to certainexample embodiments, firing conditions may be controlled to provide, forexample, greater temperature uniformity (e.g., in a range of about <2.0°C.) and sufficient heating time (e.g., in a range of about 20-30minutes) to allow the glass to stabilize and flatten by allowing theglass substrates to reach even temperature and to allow the sealmaterial to flow. The resulting VIG unit preferably has a reduced finalseal height variation, such as, for example, wherein the final edge sealheight variation is preferably less than about 0.20 mm, more preferablyless than or equal to 0.15 mm, and even more preferably less than orequal to about 0.10 mm.

FIG. 4 is an illustrative example flowchart illustrating a method ofmaking a VIG window unit according to certain example embodiments. Asshown in FIG. 4, a first glass substrate is provided S1. The glasssubstrate may be processed to provide certain structural features of atypical VIG window unit, such as, for example, spacers or pillars, orthe like. The first glass substrate may then be provided with a sealmaterial disposed, for example, and without limitation, about aperimeter of an area to be sealed and which defines a cavity with asecond glass substrate (discussed below) S3. As noted above, there maybe any number of possible frit or seal materials used to form the sealin the VIG window unit. For example, and without limitation, be of orinclude a vanadium based or VBZ type seal or a solder glass type seal.Example vanadium based or VBZ type seal compositions are disclosed inU.S. patent application Ser. No. 13/354,963, filed Jan. 20, 2012, thedisclosure of which is incorporated by reference herein in its entirety.VBZ (e.g., vanadium, barium, zinc) based seal compositions are discussedin Ser. No. 13/354,963, and may be used for the edge seal 4 in certainexample embodiments. Conventional solder glass frit material may also beused for the edge seal 4 in certain example embodiments. According tocertain preferred example embodiments, the seal material is deposited bymachine to a green frit height S3 based, for example, on a type ofsubsequent firing to be used. For example, in short-wave infrared (SWIR)firing a green unfired frit (e.g., seal material) height may preferablybe in a range of about 0.4 mm to 0.9 mm, or more preferably in a rangeof about 0.5 mm to 0.8 mm, and even more preferably about 0.6 mm to 0.7mm. As noted above, because of the relatively short time used for SWIRprocessing, the tolerance of initial green frit height deposition may belower than in the case of a longer cycle firing process. For example,and without limitation, for longer cycle convention type firing asdiscussed in greater detail above, for example, green unfired fritheights may preferably be in a range of about 0.4 mm to 1.0 mm, or morepreferably about 0.5 mm to 0.9 mm, and even more preferably about 0.6 mmto 0.9 mm, due to longer peak heating times that allows the sealmaterial to flow or settle down to the height of the pillars or spacers.After the seal material is provided S3, a second glass substrate isprovided S5 which sandwiches the pillars and unfired frit materialbetween the first and second glass substrates. The first and secondglass substrates, together with the frit seal material are then fired S7using any suitable technique, such as, for example, and withoutlimitation, SWIR or long cycle convection. The resulting VIG unitpreferably has a reduced final seal height variation, such as, forexample, the final edge seal height variation is preferably less thanabout 0.20 mm, more preferably less than or equal to about 0.15 mm, andeven more preferably less than or equal to about 0.10 mm.

Thus, in certain example embodiments of this invention, there isprovided a vacuum insulated glass (VIG) window unit comprising: a firstsubstrate and a second substrate; a seal material sandwiched between thefirst and second substrates defining a periphery of a cavity formedbetween the first and second substrates, the cavity between thesubstrates being at a pressure less than atmospheric, and the sealmaterial forming a hermetic seal between the first and secondsubstrates, wherein a variation in a height of the seal material aroundthe entire cavity is less than about 0.20 mm.

In the VIG window unit of the immediately preceding paragraph, thevariation in the height of the seal material around the entire cavitymay be less than or equal to about 0.15 mm, more preferably less than orequal about 0.10 mm.

In the VIG window unit of any of the preceding two paragraphs, there mayalso be provided a plurality of spacers disposed between said first andsecond substrates.

In the VIG window unit of any of the preceding three paragraphs, aheight of the seal material may substantially match a height of spacersbetween the substrates.

In the VIG window unit of any of the preceding four paragraphs, saidfirst and second substrates may be glass substrates.

In the VIG window unit of any of the preceding five paragraphs, saidseal material may comprise an adhesive containing frit.

In the VIG window unit of any of the preceding six paragraphs, said sealmaterial may comprise vanadium.

As used herein, the terms “on,” “supported by,” and the like should notbe interpreted to mean that two elements are directly adjacent to oneanother unless explicitly stated. In other words, a first layer may besaid to be “on” or “supported by” a second layer, even if there are oneor more layers there between.

While certain example embodiments have been described and disclosedherein, it will be understood that the embodiments described herein areintended to be illustrative, not limiting, and that those skilled in theart will understand that various modifications may be made withoutdeparting from the true spirit and full scope of the claims appendedhereto.

1-19. (canceled)
 20. A vacuum insulated glass (VIG) window unitcomprising: a first glass substrate and a second glass substrate; a sealmaterial comprising vanadium, zinc and barium, the seal materialconsisting essentially of frit and sandwiched between at least the firstand second glass substrates, and wherein a cavity between the first andsecond glass substrates is at a pressure less than atmospheric pressure,a plurality of spacers provided between at least the first and secondglass substrates; and the seal material consisting essentially of fritforming a hermetic seal, and wherein a variation in a height of the sealmaterial around the entire cavity is less than or equal to 0.15 mm. 21.The vacuum insulated glass window unit of claim 20, wherein thevariation in the height of the seal material around the entire cavity isless than or equal to 0.10 mm.
 22. The vacuum insulated glass windowunit of claim 20, wherein a height of the seal material substantiallymatches a height of said spacers.